Process for sweetening hydrocarbon oils



Patented July 16, 1940 UNITED STATES PATENT OFFICE PROCESS FOR SWEETENING HYDRO- CARBON OILS Charles M. Blair, Jr., Webster Groves, Mo., and Ira S. Boydstun, Fort Worth, Tex., assignors to Petrolite Corporation, Ltd'., Wilmington, DeL, a corporation of Delaware No Drawing. Application November 1'7, 1939, Serial No. 305,037

11 Claims.

The doctor treatment has long been applied to petroleum oils for the removal of mercaptans. It involves treatment of the oils with elementary sulfur and an aqueous alkaline solution of sodium plumbite, known as the doctor solution. The plunibite solution effects a chemical reaction between the mercaptans and the elementary sulfur, resultingin the conversion of the inercaptans to dialkyl disulfides and also into some trisulfide, while the sulfur is converted mainly into sulfides, polysulfi-des, thiosulfates, etc.

In practicing the conventional doctor treatment, an excess of elementary sulfur is used to bring about a break, a term used in the art to indicate the settling or subsidence point in the doctor treatment. That is to say, the amount of free sulfur used is in excess of the theoretical quantity required to convert the mercaptans into disulfides and other innocuous compounds, the'excess serving to induce the break in the treatment. Such use of elementary sulfur to effect settling or subsidence results in the incorporation of sulfur into the distillate, with its attendant objections. Among these objections, in the case of gasoline, are poor inhibitor and tetraethyl lead susceptibility, lowered antiknock value, increased corrosive action on metals, poor color and odor stability, and increased tendency to form gum.

Although doctor treatment in its many variations is well understood in the art, it may be well to emphasize, by a suitable reference, the circumstances and conditions attending a breakand the difiiculty of coagulating the colloidal black precipitate.

Doctor plants difier in the way in which doctor solution and sulfur are mixed with the gasoline and the length of time they remain in con- (Cl. INS-33) tact; It is common practice to add the sulfur in gasoline solution before, at the same time as, or after the gasoline and doctor solutions are mixed. The mixing may be done by orifice plates, baflled pipes, pipes with right-angle bends,

, or mechanical mixing devices,and mixing time may vary from a few seconds to several minutes.

When sulfur is added to a mixture of gasoline and doctor solution, the oil becomes orange-red in color; after a longer or shorter time, depend- 4 ing on the gasoline and the amount of sulfur added, the break takes place, when the color disappears and a red-brown to black precipitate, usually called lead sulfide, forms and settles.

In different plants, the break may be produced as the gasoline leaves the mixers or it may not occur until after the gasoline has entered the settling drum. If a plant has adequate mixing (the proper time of mixing will depend on the type of gasoline and somewhat on the degree of sourness), the gasoline may be allowed to break as it leaves the mixers, and the amount of sulfur required to do this will not be so great as to harm inhibitor susceptibility. However, if a planthas little mixing equipment (a common installation is three mixing nozzles in about six feet of line, Whichfor most gasoline is much less mixing than is desirable), a break cannot be obtained in the mixers without using a considerable excess of sulfur, with consequent detriment to the inhibitor effectiveness. If, however, the break in such plants occurs in the first settler from three to fifteen minutes .afterthe gasoline leaves the mixers, the results from an inhibitor standpoint will usually be satisfactory. But when the break occurs in the settler, the gasoline being no longer in contact with doctor solution, it tends to produce a finer precipitate, settling more slowly than whenthe gasoline is broken out while still in contact with doctor solution. As plants deficient in mixing equipment are also often lacking in settling capacity,

the treater in such cases faces a serious dilemma.

If he-uses excess sulfur, his gasoline settles well but inhibitor susceptibility is poor; if sulfur is kept down, the gasoline breaks and settles slowly and lead sulfide leaves the plant suspended in the gasoline. (Industrial & Engineering Chemistry, vol. 30, No. 11, Nov. 1938, p. 1276.)

Thus, in actual practice, the present trend has been to continue to use sulfur as a break inducer, insofar that no universal and economic solution of the problem has been heretofore available. Some effort has been made to solve the problem by subsequent washing with aqueous solution, but this has resulted in attendant loss of expensive lead. Another approach to the made to apply such process in instances where. the amount of elementary sulfur represented only theoretical quantities and which'would necessitate that the simple fatty materials, such. as soap, be relied upon solely as thebreak in ducer.

We have now found that certain esteri fication products possess the property of inducing a I break in the doctor treatment and our invention involves their use, in the sweetening of sour hydrocarbon oils by means of plumbite solution and elementary sulfur, to effect the settling or subsidence in the known sweetening process.

More specifically, the materials contemplated for use as break inducers in the present invention are represented by the partial esterification product of a polyhydric alcohol with a drastically oxidized, unsaturated. non-drying or semi-drying vegetable or animal fatty oil or fatty acid. Preferably, the break inducers are produced by re-esterification of the oxidized o1 blown fatty material of the kind mentioned, but they may also be produced in other suitable ways.

As herein used, the term polyhydric alcohols refers to aliphatic alcohols containing two or more hydroxyl groups and is intended to include such compounds as glycerol, ethylene gly: col, beta-methyl glycerol, 1,3 propanediol pentamethylene glycol, alpha, beta, gamma pentanetriol, sorbitol, mannitol, and the like, and also the polyhydroxy ether alcohols such as diglycerol, triglycerol, diethylene glycol, etc. Such polyhydric ether alcohols may also be produced by ether formation from two or more different polyhydric alcohols to yield compounds such as ethylene glycol monoglyceryl ether, l,3 propanediol monoethylene glycol ether, diethylene glycol monoglyceryl ether, etc. Suitable polyhydroxy ether alcohols may also be produced from a polyhydric alcohol containing three or more hydroxyls and a monohydric alcohol. Examples of such compounds are glycerol monobutyl ether, glycerol monoallyl ethenpentanetriol monoethyl ether, diglycerol monopropyl ether, etc.

The break inducers of this invention. are pro duced from drastically oxidized castor oil and other drastically oxidized unsaturated, non-drying or semi-drying vegetable and animal oils, such as soy-bean oil, rapeseed oil, cottonseed oil, sunfiowerseed oil, corn oil, neats-foot oil, and the like. These oils are to be distinguished from the.

drying oils, such as linseed oil, tung oil, oiticica oil, poppyseed oil, and perilla oil, and from the saturated non-drying oils and fats, such as stearine, and also from the oxidized derivatives of fish oils or marine animal oils.

Drastically oxidized vegetable and animal oils fatty oils by means of a gaseous medium, such as air, oxygen, ozone, or ozonized air. The gaseous medium, such as air, may be moist or dry; and oxidation may take place in the presence or absence of a catalyst. The catalyst may be of a metallic type, such as lead oleate, cobalt ricinoleate, manganese linoleate, etc., or it may be of the organic type which produces peroxides, such as alpha pinene, linseed oil, etc. Oxidation may take place at atmospheric pressure or at superatmospheric pressure, i. e., pressures up to or including 200 pounds per square inch, and at any temperature slightly above the boiling point ot water, for instance, C. up to any temthe longer time periods being employed generally when the temperature is low and oxidation is brought about with air at atmospheric pressure. 'Mild oxidation, i. e., oxidation as exemplified by the exposure of a film of semi-drying oil or castoroil to air for an extended period of time, such as weeks or even months (see Chemical Technology and Analysis of Oils, Fats, and Waxes, by Lewkowitsch, sixth edition, volume 2, page 406), produces relatively small changes in certain chemical indices, such as iodine value, the acetyl value, and the saponification value. If drastic oxidation takes place either by continued mild oxidation or by more vigorous oxidation from the very beginning of the reaction as induced by either a higher reactive temperature or the presence of a catalyst, one then obtains an oxidized oil having chemical and physical characteristics which clearly indicate that drastic oxidation has taken place. These indiccs of drastic oxidation, compared to the original oil, are generally a lowered iodine value, an increased saponification value, an increased gravity, and an increased refractive index.

Drastically oxidized castor oil or drastically oxidized semi-drying oils can be prepared by well-known methods or can be purchased in the open market under various trade names, such as blown oils, blended oils, blended bodied oils, processed castor oil, oxidized castor oil, oxidized corn oil, blown sunflowerseed oil, blown soybean oil/heavy blown rapeseed oil, viscous oil, etc.

The esters contemplated for use as break inducers in the presentprocess are most suitably prepared by direct re-esterification reactions between a polyhydric alcohol and the oxidized castor oil or oxidized semi-drying oil. The proportions of polyhydric alcohol to oxidized fatty oil and the conditions of reaction must be such that they do not lead to esterification of all the available hydroxyls of the polyhydric alcohols. This re-esterification reaction in general may be carried out by heating the polyhydric alcohol kind and the amount of polyhydric alcohol originally employed in the reaction. Suitable break inducers, which are only very slightly sol-- uble or insoluble in water, may, however, be produced by this reaction.

'It will, of course, be understood that the break s inducer need not necessarily-be an esterification product of a blown oil but may suitably be a fractional ester of a polyhydric alcohol with a blown or oxidized fatty acid,-such as castor oil fatty acid, soya bean oil fatty acid, oleic acid, etc. Instead of re-esterification of a blown oil, the break inducer may be produced in other ways, such as by oxidizing or blowing a fatty acid, for example, oiei'c acid, and then combining the blownacid with a suitable polyhydric alcohol to yield a hydroxylated ester. However, re-esterification of blown oils is our preferred method of making the break inducers since it is the simplest and most economical method available.

Esters obtained by re-esterification of blown or oxidized fatty oils with glycerol are often referred to as superglycerinated blown oils. Many such super-glycerinated blown oils, as well as similar products obtained from other polyhydric alcohols, are regular articles of commerce available on the open market. 4

Our preferred break inducer is the product obtained by re-esterification of drastically oxidized, pale blown castor oil with glycerol. This product may be obtained by heating, at a temperature of 200-250 C. for a periodof hours, about 600 parts commercial glycerin with about 1000 parts drastically oxidized pale blown castor oil having the following characteristics:

Acid number 15.1 to 25.0 Saponification number 230.5 to 274.0 Iodine number 43.5 to 55.0 Acetyl number 164.0 to 192.0 Hydroxyl number -l 188.0 to 220.0 Percent unsaponifiable matter 1.1

' Percent nitrogen 0.0 Percent S03 0.0

Percent ash Trace The break inducers described may be used as such or, if desired, some of the residual hydroxyls attached to the polyhydric alcohol residue may be esterified with aliphatic monocarboxy acids elementary sulfur employed in the doctor treatment is not in excess of the theoretical amount required to convert the mercaptans. In this preferred operation, where no appreciable excess of sulfur is used in the doctor treatment, there is effected a faster break than can be obtained by means of other break inducers and frequently a break is effected where one might not be otherwise obtainable. Additionally, there is recovered a distillate which is free of excess sulfur, an important advantage as has already been indicated.

However, the invention is not limited to the use of the organic compounds referred to as the sole break inducer but they may be employed in conjunction with other substances having a like property, such as elementary sulfur. In operation of this type, a small excess of sulfur would be used in the doctor treatment, the excess functioning with the compounds of this invention to bring about the desired break in the treatment. The advantages of such op ment no excess of sulfur capable of completely or partially acting as a break inducer. Elementary sulfur, if present in sufiicient excess in the sweetened distillate, can be detected by the doctor test with the addition of a mercaptan such as ethyl of butyl mercaptan. For instance, a

gasoline containing an excess of elementary sulfur no longer shows positive in the doctor test. However, if there is a slight excess of elementary sulfur present, this elementary sulfurcan be detected by the addition of butyl mercaptan or the like, followed by a doctor test on the. admixture. A large excess may be indicated bythe less sensitive copper strip test.

The butyl inercaptan test, referred to above, is commonly used in a qualitative manner to detect excess elementary sulfur. This test is described in the Universal Oil Products Co. Bulletin No. 22, p. 15, as follows:

In doctor sweetening, the most important factor in securing inhibitor effectiveness, is to use the smallest possible amount of sulfur. Sulfur addition may be controlled by testing with mercury or butyl mercaptan. In making the butyl inercaptan test, a sample of gasoline drawn from the doctor plant after it has left the mixers is allowed to stand until the lead sulfide has settled, and cc. filtered into a 4 ounce oil sample bottle. '20 cc. of a l. to 1,400 solution of butyl mercaptan is added and 10 cc. of doctor solution. The mixture is shaken for 15 seconds and observed. The sample should be green-yellow. It will slowly become opaque but should remain yellow in color even if observed for 30 minutes. If it turns orange or brown, excess sulfur has been used, and on addition of inhibitor the gasoline will have lower induction period and higher copper-dish gum than would have resulted had less sulfur been used.

The chemistry of the reactions which enter into doctor sweetening is rather complex and not completely understood. However, it is common practice, for the purpose of calculating the amount of sulfur necessary, to use the following reaction as being representative:

With distillates where these reactions take place, the theoretical sulfur requirement may be calculated by use of the above equations and the known original mercaptan content of the distillate. However, for all'practical purposes, the butyl mercaptan test, previously described, may be used as a test for whetheror not excess sulfur has been used. Accordingly, the term negative to the butyl mercaptan test, as applied to sweetened distillates, is used herein to mean that a distillate has been sweetened with the theoretical amount of sulfur, or that the minimum amount of sulfur necessary for completion of the sweetening reaction has been employed. The reason for this is that the butyl mercaptain test may-be made more easily and more quickly than a determination of the actual course or nature of the sweetening reactions.

As is understood, of course, if hydrogen sulfide is present, allowance must be made for the amount of lead required to remove such sulfide. However, this is not apt to be a factor requiring consideration, due to usual preliminary removal of hydrogen sulfide.

In view of what has been said previously, it is obvious that the satisfactory application of the doctor treatment must involve a rapid and complete separation of lead sulfide and associated insoluble material, as soon as the mercaptans are converted into disulfides or other more innocuous compounds. Although the above reactions indicate only precipitation of lead sulfide, it has been found that in reality a precipirate may contain a comparatively small amount of lead sulfide; and there may also be present various complex materials, part of which at least are organic in nature and may represent basic mercaptides. The equations indicate that the amount of elementary sulfur to'be added per pound of combined sulfur present as mercaptan should be in the ratio of one-half to one. In actual practice, however, with the conventional doctor treatment, the quantity of sulfur added for complete reaction, and particularly to give subsidence or settling of the black precipitate, is not so definite. As a matter of common practice, sulfur isadded in the conventional doctor treatment for two distinct purposes of converting mercaptans and inducing the break; and these two purposes must be fully appreciated in order to understand the benefit obtained by applying the improved procedure which constitutes our present invention, particularly in its preferable form, i. e., where the complex organic compounds herein described are used as the sole break inducer, with only the theoretical amount of sulfur to convert mercaptans or to give a negative butyl mercaptan test.

It has heretofore been proposed to employ water soluble soaps to effect the break in doctor treatment, the soaps being utilized in ratios of 1 to 2500 or 1 to 7500. At such ratios, the commonsoaps are often ineffective and hence there is the tendency to employ just as much sulfur as if no soap had been added. In contradistinction to the common soaps heretofore contemplated, the break inducers of the present invention are invariably effective and invariably enable a marked reduction in the amount of sulfur needed in the doctor treatment, even to the extent, as in the preferred embodiment already described, of limiting the sulfur to the theoretical amount necessary for converting the mercaptans into innocuous compounds.

The break inducers of this invention need be used in only very minute quantities, for example, in ratios varying from 1 to 5000 or 1 to I500 or even 1 to 75,000 based on recovered or sweetened gasoline or other distillate treated. To the extent that our improved break inducers possess the property of forming oil-in-water emulsions, it should be observed that they are employed in such insignificant quantities that they do not exhibit any detectable or appreciable emulsifying action.

Although our invention can be applied to any variation of the conventional doctor treatment in a manner which is most convenient under the specific conditions surrounding the particular operation, for purposes of brevity, we will describe only the preferable form of procedure, i. e., where the herein disclosed organic compounds are used as sole break inducers. It is obvious, however, that those skilled in the art and acquainted with such procedure could readily modify the conventional doctor treatment in which elementary sulfur is used as a break inducer, so as to reduce the amount of sulfur employed, and offset that reduction by suitable quantities of the break inducers of this invention.

In a continuous doctor sweetening plant, the organic-break inducer is added continuously to the stream of sour distillate prior to its admixture with doctor solution and sulfur. When the break inducer is a liquid, this is conveniently done by means of a small injector pump adjusted to deliver the break inducer in some definite, desired amount, usually within the limits of one part per 7500 to 75,000 parts of gasoline. After the introduction of break inducer has begun, the amount of sulfur added to the distillate, or to the mixture of distillate and doctor solution, is decreased to the theoretical amount.

In batch system doctor sweetening plants, the required amount of break inducer is introduced into the sour distillate and mixed thoroughly before the treatment with doctor solution and sulfur. In this case, also, the amount of sulfur used is reduced to the theoretical amount.

Sometimes better results are obtained if the break inducer is added to the doctor solution or to the distillate after the latter has been mixed with doctor solution and sulfur. Regardless of the point of introduction of the break inducer,

however, the amount of sulfur required for completion of the sweetening reactions and subsidence of the black precipitate is reduced to, or nearly to, the theoretical amount.

The doctor solution used for sweetening is generally regenerated after each use and employed for sweetening further amounts of sour distillate. Where the break inducer has been added to the doctor solution, its activity may persist thru one 'or more regenerations, but eventually further amounts will have to be added. The number of volumes of distillate sweetened per volume of break inducer used in the doctor solution usually will be, more than 7500, and the ratio of break inducer may average one part to 25,000 parts sweetened distillate.

In order to indicate the effectiveness of the present process, attention is directed to the following table. The gasoline employed in the present instance was obtained from East Texas crude petroleum. The figures given refer totests made present, or when the gasoline gives a positive with 100 gram portions of gasoline:

butylmercaptan test. In each instance, the break Ratio of l .i

Mg. of Actual break in- Butyl mersulfur re- Mg. oi Character of Doctor test quired sulfur Breakmduwused ggggggggg break on m mas gg gg g f g g (theory) re uired treated 3. 0 3. 0 None 0 3.0 4.0 None 0 3. 0 5. 0 None 0 Positive. 3. 0 3. 0 Sodium steara 0. 0002 Do. 3.0 4.0 do 0. 0002 Positive. 3.0 3.0 Sodium oleate 0. 0002 Do. 3. 0 '4. 0 do 0.0002 Positive. 3. 0 3. 0 Sodium resinate. 0.0002 I Do. 3. 0 4. 0 do 0. 0002 Positive. 3.0 3.0 Oastile soap... 0. 0002 Do. 3.0 4. .0 -do .Q 0; 0002 Positive. 3. 0 3. O Glycerol reesterified pale 0. 00005 Negative.

blown castor oil. 3. 0 3.0 Glycerol reesterified blown 0. 00005 Do. soyabean oil.

Examination of the above table emphasizes the numerous salient points previously discussed. For instance, reference is madeto those tests inthe above table which are concerned with the use of the common, rather simple, type of break inducer, to wit, materials such as sodium stearate, sodium oleate, castile soap, sodium resinate and the like.

Furthermore attention is directed to the first three tests which indicate the results obtained when sulfur alone is used as the break inducer. It'is to be noted that in the tests as conducted, it was necessary to use three milligrams of sulfur in order to complete the chemical reactions. On the other hand, the addition of 33% excess of sulfur, i. e., t-he use of 4 milligrams of elementary sulfur, did'not give a break. However, when the amount of sulfur used was increased to 5 milligrams, i. e., a (ES excess, then a perfectly satisfactory break was obtained. Obviously such excess of elementary sulfur resulted in a positive butyl mercaptan test. When an effort was made to substitute the common soap type of break inducer for elementary sulfur, it was found that its use, in amount equivalent to times the amount of sulfur required for break induction, did not give satisfactory results. For instance, when the 2 milligram excess of elementary sulfur was replaced by milligrams of sodium stearate, a good break was not obtained. This same condition prevailed when a similar amount of sodium oleate or sodium resinate or castile soap was employed. When there was added only the amount of elementary sulfur required to complete the chemical reaction and it was attempted to depend on the addition of sodium stearate, sodium oleate, castile soap or sodium resinate, as sole break inducers, a satisfactory break was not obtained even when these compounds were employed in a ratio of l to 5000. In comparison to the results above indicated, attention is directed to the results obtained when employing the break inducers herein contemplated for use in the doctor treatment.

It is to be noted that the break inducers of this invention were used in a ratio of 1 to 20,000 and in each case, an excellent break was obtained even though there was no sulfur available for break induction, or to say it in another way, when the amountof sulfur employed was only sufficient to complete the chemical reactions involved. In each instance, since there Was no excess sulfur employed, the butyl meicaptan test obviously has to be negative. Since the butyl mercaptan test had to be negative, it followed that the gasoline was of a type which was free from certain inherently objectionable qualities which are common when there is an excess of elementary sulfur obtained was the kind characterized as being good, i. e.,' appeared to be satisfactory under any condition of plant operation which one would ordinarily employ.

We have previously indicated that the amount of added break inducer may be as low as one part in 75,000 parts ofv the oil being sweetened. In

practice, however, the amount of break inducer actually present in the oil may be even less than this during certain phases of the process. For example, in an operation involving recirculation of doctor solution, the ratio of break inducer in the first batch of oil may not exceed one to 30,000 or even one to 45,000 but recycling of the doctor solution once or twice, without further addition of break inducer, may result in an actual ratio of 1-80,000 or l-90,000 or even a ratio in excess of l100,000 in subsequent batches of oil. Therefore, it is to be understood that the heretofore mentioned ratio of 1-75,000 is not the upper limit of effectiveness, particularly in a recirculation process.

It will be further understood that, instead of employing a single break inducer of the kind herein disclosed, a mixture of two or more of them may be used, if desired. Indeed, the process of manufacturemay result in the production of a mixture of a number of break-inducing compounds rather than a single compound in a technically or chemically pure state. Moreover, a break inducer of this invention may be employed in admixture with other types of break inducers for which We have filed separate applications.

Frequently, the compounds of this invention have beneficial effects in addition to bringing about rapid subsidence. For example, as a result of their use, the amount of black strap or feathery material appearing at interfacial surfaces may be greatly diminished or entirely eliminated.

It is to be understood that the detailed disclosures herein are for illustrative purposes only and are not to be considered as limitations on the invention, inasmuch as various modifications within the scope of the appended claims will be apparent to those skilled in the art.

Having described our invention, we claim:

1. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the method of inducing a break in the doctor treatment which comprises adding a partial esterification product of a polyhydric alcohol with a drastically oxidized fatty body; said fatty body being selected from the group consisting of the unsaturated non-drying and semi-drying vegetable and animal fatty substances containing an ester-forming group.

characterized'in that said fatty body 21 The method as defined in claim 1 further comprises an ester.

3. A method for sweetening hydrocarbon oils containing mercaptans which comprises treating.

the oil with doctor solution and a quantity of elementary sulfur not appreciably in excess of the theoretical amount requiredto convert themercaptans into innocuous compounds, and inducing a break in said treatment by the addition of a partial esterification product of a polyhydric alcohol with a drastically oxidized fatty body, said fatty body being selected from the group consisting of the unsaturated non-drying and semi-drying vegetable and animal fatty substances containing an ester-forming group.

' 4. The method as defined in claim 3 further characterized in that said fatty body comprises an .ester.

containing mercaptans which comprises con- 'verting the mercaptans into innocuous compounds by treatment of the oil with alkaline plumbite solution and elementary sulfur, the amount of sul- Lfur'being insufficient to render the oil positive to the butyl mercaptan test and insufiicient to effect settlingor subsidence, and inducing a break in said treatmen't'by adding a partial esterification product of a polyhydric alcohol with a drastically oxidized fatty body, said fatty body being selected from the group consisting of the unsaturated nondrying and semi-drying vegetable and animal fatty substances containing an ester-forming group.

5. A method for sweeteninghydrocarbon oils 6. In the sweetening'of sour hydrocarbon oils by treatment with doctor solution and. elementary sulfur, the improvement which comprises facilitating the break in said treatment by the addition of a partial esterification productlof a polyhydric alcohol with a drastically oxidizedfatty body selected from. the group consisting of the unsaturated, non-drying and semi-drying animal and vegetable fatty substances containing an. ester- 10. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the improvement which comprises facilitating the break in said treatment by the addition of the partial esterification product of drastically oxidized castor oil with glycerol.

11. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the improvement which comprises facilitating the break in said treatment by the addition of the partial esterification product of drastically 30 oxidized soyabean oil with glycerol.

CHARLES M. BLAIR, JR. IRA S. BOYDSTUN. 

